UV-cross-linked laminating adhesive

ABSTRACT

A composition comprising an aqueous polymer dispersion, characterised in that a) the composition contains 0.001 to 0.5 mol of a photo-initiator, which causes a cross-linking reaction on irradiation with energy-rich light and b) the polymer dispersed in the dispersion has 0.0001 to 1 mol of keto or aldehyde groups, whereby the mol amounts relate to 100 g of the dispersed polymer.

The invention relates to a composition comprising an aqueous polymerdispersion, wherein

-   -   a) the composition contains from 0.0001 to 0.5 mol of a        photoinitiator which on exposure to high-energy light brings        about a crosslinking reaction, and    -   b) the polymer dispersed in the dispersion has from 0.0001 to 1        mol of keto or aldehyde groups,        the molar data being based in each case on 100 g of the        dispersed polymer.

The invention further relates to the use of the composition as anadhesive, especially for high gloss film lamination, and to a method ofhigh gloss film lamination.

Crosslinkable adhesives are frequently used in high gloss filmlamination. In high gloss film lamination, first a transparent polymerfilm, generally oriented polypropylene OPP or else polyacetate, iscoated with the liquid adhesive. Then the adhesive is dried and thecoated film is then laminated, using pressure and heat, to the printedmaterial, generally a printed card or paper. The resultant laminate isfrequently grooved or embossed during further processing. For stabilityduring grooving or embossing the adhesive layer must withstand thesedeformations of the laminate, and in the groove or at the embossedpoints there must be no separation of the gloss film from the printedmaterial. To ensure this, chemically crosslinked adhesive systems aregenerally used. Since the crosslinking systems usually employed hererequire time to build up the necessary cohesion in the adhesive layer,the laminates produced must firstly be stored for some hours before theycan be grooved or embossed. This intermediate storage is increasinglyperceived as a disadvantage, since it means delaying work on orders.

Chemically crosslinking polymer dispersions for high gloss filmlamination are known, for example, from EP-A-148386 or EP-A644902.

DE-A-19916663 discloses UV-crosslinkable polymer dispersions asadhesives for high gloss film lamination. With these adhesives as wellthe quality of the resulting laminate depends on the duration ofintermediate storage of the adhesive-coated films. As the storage periodgoes on, the quality becomes poorer.

It is an object of the present invention to provide adhesives for highgloss film lamination where the quality of the resulting laminates isindependent of the storage time of the coated films.

The laminates obtained are to have high strength, high gloss, and goodadhesion, even in the area of grooves or embossments in the card.

We have found that this object is achieved by means of the compositionsdefined at the outset and their use.

The composition of the invention comprises an aqueous dispersion of apolymer which can be crosslinked by UV radiation.

For this purpose the composition comprises a photoinitiator. Onirradiating with high-energy light, in particular UV light, thephotoinitiator brings about crosslinking of the polymer, preferably by achemical grafting reaction of the photoinitiator with a spatiallyadjacent polymer chain. In particular, the crosslinking may take placeby insertion of a carbonyl group of the photoinitiator into an adjacentC—H bond, forming a —C—C—O—H group.

The composition comprises from 0.0001 to 0.5 mol, particularlypreferably from 0.0002 to 0.1 mol, very particularly preferably from0.0003 to 0.01 mol, of the photoinitiator, or molecule group active asthe photoinitiator, per 100 g of polymer.

The photoinitiator comprises for example acetophenone, benzophenone,benzoin ethers, benzil dialkyl ketals or derivatives thereof.

The photoinitiator is preferably bonded to the polymer dispersed in theaqueous dispersion (called simply polymer hereinbelow).

The photoinitiator particularly preferably comprises a photoinitiatorwhich has been incorporated into the polymer chain by free-radicalcopolymerization. For this purpose the photoinitiator preferablycomprises an acrylic or methacrylic group.

Suitable copolymerizable photoinitiators are derivatives of acetophenoneor benzophenone which contain at least one, preferably one,ethylenically unsaturated group. The ethylenically unsaturated grouppreferably comprises an acrylic or methacrylic group.

The ethylenically unsaturated group may have direct bonding to thephenyl ring of the derivative of acetophenone or of benzophenone. Thereis generally a spacer group (spacer) between the phenyl ring and theethylenically unsaturated group.

The spacer group may, for example, contain up to 100 carbon atoms.

Suitable acetophenone derivatives or benzophenone derivatives aredescribed, for example, in EP-A-346 734, EP-A-377199 (claim 1), DE-A-4037 079 (claim 1) and DE-A-3 844 444 (claim 1) and are also disclosed inthe present application by way of this reference. Preferred acetophenonederivatives and benzophenone derivatives have the formula

where R¹ is an organic radical having up to 30 carbon atoms, R² is ahydrogen atom or methyl and R³ is unsubstituted or substituted phenyl orC₁–C₄ alkyl.

R¹ is particularly preferably alkylene, in particular C₂–C₈ alkylene.

R³ is particularly preferably methyl or phenyl.

The polymer further contains from 0.0001 to 1 mol, preferably from0.0002 to 0.10 mol, with particular preference from 0.0006 to 0.03mol,of keto or aldehyde groups.

The keto or aldehyde groups are preferably attached to the polymer bycopolymerization of copolymerizable, ethylenically unsaturated compoundscontaining keto or aldehyde groups. Suitable compounds of this kindinclude acrolein, methacrolein, vinyl alkyl ketones having from 1 to 20,preferably from 1 to 10, carbon atoms in the alkyl radical, formylstyrene, alkyl (meth)acrylates having one or two keto or aldehyde groupsor one keto group and one aldehyde group in the alkyl radical, the alkylradical preferably containing a total of from 3 to 10 carbon atoms,e.g., (meth)acryloyloxyalkylpropanals, such as are described inDE-A-2722097. Also suitable, furthermore, areN-oxoalkyl(meth)acrylamides such as are known, for example, from U.S.Pat No. 4,226,007; DE-A-2061213 or DE-A-2207209.

Particular preference is given to acetoacetyl (meth)acrylate,acetoacetoxyethyl (meth)acrylate, and, in particular,diacetoneacrylamide.

The polymer has preferably been built up from free-radicallypolymerizable compounds (monomers).

Preferably at least 40% by weight of the polymer, particularlypreferably at least 60% by weight, very particularly preferably at least80% by weight, is composed of principal monomers.

The principal monomers are selected from the group consisting of C₁–C₂₀alkyl (meth)acrylates, vinyl esters of carboxylic acids containing up to20 carbon atoms, vinylaromatics having up to 20 carbon atoms,ethylenically unsaturated nitriles, vinyl halides, vinyl ethers ofalcohols containing from 1 to 10 carbon atoms, aliphatic hydrocarbonshaving from 2 to 8 carbon atoms and 1 or 2 double bonds, and mixtures ofthese monomers.

Mention may be made, for example, of alkyl (meth)acrylates having aC₁–C₁₀ alkyl radical, such as methyl methacrylate, methyl acrylate,n-butyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate.

Mixtures of the alkyl (meth)acrylates are also particularly suitable.

Examples of vinyl esters of carboxylic acids having from 1 to 20 carbonatoms are vinyl laurate, vinyl stearate, vinyl propionate, Versatic acidvinyl esters, and vinyl acetate.

Possible vinylaromatic compounds are vinyltoluene, α- andp-methylstyrene, α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene,and, preferably, styrene. Examples of nitriles are acrylonitrile andmethacrylonitrile.

The vinyl halides are chlorine-, fluorine- or bromine-substitutedethylenically unsaturated compounds, preferably vinyl chloride andvinylidene chloride.

Examples of vinyl ethers which may be mentioned are vinyl methyl etherand vinyl isobutyl ether. Preference is given to vinyl ethers ofalcohols containing from 1 to 4 carbon atoms.

As hydrocarbons having from 2 to 8 carbon atoms and two olefinic doublebonds, mention may be made of butadiene, isoprene and chloroprene.

Preferred principal monomers are the C₁–C₁₀ alkyl acrylates and C₁–C₁₀alkyl methacrylates, in particular C₁–C₈ alkyl acrylates and C₁–C₈ alkylmethacrylates, and in each case the acrylates are particularlypreferred.

Very particular preference is given to methyl acrylate, ethyl acrylate,n-butyl acrylate, n-hexyl acrylate, octyl acrylate and 2-ethylhexylacrylate, and also to mixtures of these monomers.

The polymer further contains, preferably, abovementioned monomerscontaining a photoinitiator group and abovementioned monomers containinga keto or aldehyde group, in amounts such that the desired amount ofthese groups is present in the polymer.

Besides the principal monomers above, the polymer may contain othermonomers, e.g., monomers with carboxylic acid, sulfonic acid orphosphonic acid groups. Carboxylic acid groups are preferred. Exampleswhich may be mentioned are acrylic acid, methacrylic acid, itaconicacid, maleic acid, and fumaric acid.

Examples of other monomers are monomers containing hydroxyl groups, inparticular C₁–C₁₀ hydroxyalkyl (meth)acrylates, and (meth)acrylamide.

Other monomers which may additionally be mentioned are phenyloxyethylglycol mono(meth)acrylate, glycidyl acrylate, glycidyl methacrylate, andamino (meth)acrylates, such as 2-aminoethyl (meth)acrylate.

Monomers which carry other functional groups in addition to the doublebond, e.g., isocyanate groups, amino groups, hydroxyl groups, amidegroups or glycidyl groups, may, for example, improve the adhesion tosubstrates.

The glass transition temperature of the polymer is preferably below 60°C., in particular from −50 to +60° C., particularly preferably from −30to +40° C., and very particularly preferably from −30 to +20° C.

The glass transition temperature of the polymer may be determined byconventional methods, such as differential thermal analysis ordifferential scanning calorimetry (see, for example, ASTM 3418/82,midpoint temperature).

The polymer is preferably prepared by emulsion polymerization and istherefore an emulsion polymer.

However, it may also be prepared, for example, by solutionpolymerization, followed by dispersion in water.

Surface-active compounds used in the emulsion polymerisation are ionicand/or nonionic emulsifiers and/or protective colloids or, respectively,stabilizers.

A detailed description of suitable protective colloids is found inHouben-Weyl, Methoden der organischen Chemie, Vol. XIV/1,Makromolekulare Stoffe, Georg-Thieme-Verlag, Stuttgart, 1961, pp.411–420. Emulsifiers which may be used are either anionic, cationic orelse nonionic emulsifiers. Preferably, the auxiliary surface-activesubstances used are exclusively emulsifiers, whose molar mass is usuallybelow 2000 g/mol, unlike that of the protective colloids. If mixtures ofsurface-active substances are used, the individual components must, ofcourse, be compatible with one another, and in case of doubt this can bechecked using a few preliminary experiments. Preference is given to theuse of anionic and nonionic emulsifiers as surface-active substances.Examples of commonly used auxiliary emulsifiers are ethoxylated fattyalcohols (EO units: from 3 to 50, alkyl: C₈–C₃₆), ethoxylated mono-, di-and trialkylphenols (EO units: from 3 to 50, alkyl: C₄–C₉), alkali metalsalts of dialkyl esters of sulfosuccinic acid, and also the alkali metaland ammonium salts of alkyl sulfates (alkyl: C₈–C₁₂), of ethoxylatedalkanols (EO units: from 4 to 30, alkyl: C₁₂–C₁₈), of ethoxylatedalkylphenols (EO units: from 3 to 50, alkyl: C₄–C₉), of alkylsulfonicacids (alkyl: C₁₂–C₁₈), and of alkylarylsulfonic acids (alkyl: C₉–C₁₈).

Other suitable emulsifiers are compounds of the formula II

where R⁵ and R⁶ are hydrogen or C₄–C₁₄ alkyl but are not simultaneouslyhydrogen, and C and Y may be alkali metal ions and/or ammonium ions. R⁵and R⁶ are preferably linear or branched alkyl having from 6 to 18carbon atoms or hydrogen and in particular having 6, 12 or 16 carbonatoms, R⁵ and R⁶ not both being simultaneously hydrogen. X and Y arepreferably sodium, potassium or ammonium ions, sodium being particularlypreferred. Particularly advantageous compounds II are those in which Xand Y are sodium, R⁵ is branched alkyl having 12 carbon atoms and R⁶ ishydrogen or R⁵. Use is frequently made of industrial mixtures which havea proportion of from 50 to 90% by weight of the monoalkylated product,for example Dowfax® 2A1 (trademark of Dow Chemical Company).

Suitable emulsifiers may also be found in Houben-Weyl, Methoden derorganischen Chemie, Vol. 14/1, Makromolekulare Stoffe, Georg Thiemeverlag, Stuttgart, 1961, pages 192–208.

Examples of tradenames of the above-mentioned emulsifiers are Dowfax® 2A1, Emulan® NP 50, Dextrol® OC 50, Emulgator 825, Emulgator 825 S,Emulan® OG, Texapon® NSO, Nekanil® 904 S, Lumiten® I-RA, Lumiten E 3065,Disponil FES 77, Lutensol AT 18, Steinapol VSL, and Emulphor NPS 25.

The surface-active substance is usually used in amounts of from 0.1 to10% by weight, based on the monomers to be polymerized.

Examples of water-soluble initiators for the emulsion polymerization areammonium and alkali metal salts of peroxodisulfuric acid, e.g., sodiumperoxodisulfate, and hydrogen peroxide and organic peroxides, such astert-butyl hydroperoxide. Reduction-oxidation (redox) initiator systemsare particularly suitable.

Redox initiator systems are composed of at least one, usually inorganicreducing agent and an inorganic or organic oxidant.

The oxidation component is, for example, one of the initiators mentionedabove for the emulsion polymerization.

The reducing components are, for example, alkali metal salts ofsulfurous acid, such as sodium sulfite and sodium hydrogensulfite,alkali metal salts of disulfurous acid, such as sodium disulfite,bisulfite addition compounds of aliphatic aldehydes and ketones, such asacetone bisulfite, or reducing agents such as hydroxymethanesulfinicacid and its salts, or ascorbic acid. The redox initiator systems may beused accompanied by soluble metal compounds whose metallic component canoccur in more than one valence state.

Examples of usual redox initiator systems are ascorbic acid/iron(II)sulfate/sodium peroxodisulfate, tert-butyl hydroperoxide/sodiumdisulfite and tert-butyl hydroperoxide/Na hydroxymethanesulfinate. Theindividual components, e.g., the reducing component, may also bemixtures, e.g., a mixture of the sodium salt of hydroxymethanesulfinicacid and sodium disulfite.

The compounds mentioned are usually used in the form of aqueoussolutions, the lower concentration being determined by the amount ofwater acceptable in the dispersion and the upper concentration by thesolubility in water of the particular compound. The concentration isgenerally from 0.1 to 30% by weight, preferably from 0.5 to 20% byweight, particularly preferably from 1.0 to 10% by weight, based on thesolution.

The amount of the initiators is generally from 0.1 to 10% by weight,preferably from 0.5 to 5% by weight, based on the monomers to bepolymerized. It is also possible to use more than one differentinitiator in the emulsion polymerization.

Regulators may be used in the polymerization, for example in amounts offrom 0 to 0.8 part by weight, based on 100 parts by weight of themonomers to be polymerized, and these reduce the molecular weight.Examples of suitable compounds are those with a thiol group, such astert-butyl mercaptan, ethylhexyl thioglycolate, mercaptoethanol,mercaptopropyltrimethoxysilane and tert-dodecyl mercaptan. Theproportion of these regulators, where the composition is for use as anadhesive for composite film lamination, is in particular from 0.05 to0.8 part by weight, preferably from 0.1 to 0.5 part by weight, based on100 parts by weight of the monomers to be polymerized. For use as anadhesive for high gloss film lamination, the inclusion of a regulator isless preferred. The regulators do not contain any polymerizable,ethylenically unsaturated groups. The regulators bring about atermination of the polymerization chain and are therefore bondedterminally onto the polymer chains.

The emulsion polymerization generally takes place at from 30 to 130° C.,preferably from 50 to 90° C. The polymerization medium may be composedeither exclusively of water or of mixtures of water and liquids, such asmethanol, which are miscible therewith. It is preferable to useexclusively water. The emulsion polymerization may be carried out eitheras a batch process or as a feed process, and this includes stepped orgradient procedures. reference is given to the feed process in which aportion of the polymerization mixture forms an initial charge, is heatedto the polymerization temperature and begins to polymerize, and theremainder of the polymerization mixture is then fed into thepolymerization zone, usually via more than one spatially separate feedstreams, of which one or more comprise(s) the monomers in pure or inemulsified form, these feed streams being supplied either continuously,or in stages, or under a concentration gradient, during which thepolymerization is maintained. A seed polymer may be included in theinitial polymerization charge in order, for example, to achieve betterregulation of particle size.

The manner in which the initiator is added to the polymerization vesselin the course of the free-radical aqueous emulsion polymerization isknown to the person of average skill in the art. It can either beincluded entirely in the initial charge to the polymerization vessel orelse added, continuously or in stages, at the rate at which it isconsumed in the course of the free-radical aqueous emulsionpolymerization. In detail, this will depend both on the chemical natureof the initiator system and on the polymerization temperature. It ispreferable to include a portion in the initial charge and to supply theremainder to the polymerization zone at the rate at which it isconsumed.

In order to remove residual monomers, it is usual to add initiator aftercompletion of the actual emulsion polymerization, i.e., after a monomerconversion of at least 95%.

In the feed process, the individual components can be added to thereactor from above, through the side or from below, through the base ofthe reactor.

The emulsion polymerization gives aqueous dispersions of the polymer,generally with solids contents of from 15 to 75% by weight, preferablyfrom 40 to 75% by weight.

For a high space-time yield from the reactor, preference is given todispersions with a very high solids content. In order to be able toachieve solids contents >60% by weight, a bimodal or polymodal particlesize should be established, since otherwise the viscosity becomes toohigh and the dispersion can no longer be handled. A new particlegeneration can be produced, for example, by adding seed (EP 81083), byadding excess amounts of emulsifier, or by adding miniemulsions. Anotheradvantage associated with the low viscosity at high solids contents isimproved coating behavior at high solids contents. One or more newgenerations of particles can be produced at any desired time, dependingon the particle size distribution required for low viscosity.

The polymer is used in the form of its aqueous dispersion.

The composition preferably further comprises a compound containing atleast 2 functional groups, in particular from 2 to 5 functional groups,with particular preference 2 or 3 functional groups, with veryparticular preference 2 functional groups, which undergo a crosslinkingreaction with keto or aldehyde groups.

Examples of suitable functional groups include hydrazide, hydroxylamineor oxime ether or amino groups.

Suitable compounds containing hydrazide groups are, for example,polycarboxylic hydrazides having a molar weight of up to 500 g/mol.

Particularly preferred hydrazide compounds are dicarboxylic dihydrazidescontaining preferably from 2 to 10 carbon atoms.

Examples that may be mentioned include oxalic dihydrazide, malonicdihydrazide, succinic dihydrazide, glutaric acid dihydrazide, adipicdihydrazide, sebacic dihydrazide, maleic dihydrazide, fumaricdihydrazide, itaconic dihydrazide and/or isophthalic dihydrazide. Ofparticular interest are the following: adipic dihydrazide, sebacicdihydrazide, and isophthalic dihydrazide.

Suitable compounds containing hydroxylamine groups or oxime ether groupsare specified, for example, in WO 93/25588.

The compounds preferably comprise hydroxylamine derivatives of theformula(H₂N—O

₂A  I,where A is a saturated or unsaturated aliphatic, linear or branchedhydrocarbon radical of 2 to 12 carbon atoms, which may be interrupted byfrom 1 to 3 nonadjacent oxygen atoms, and n is 2, 3 or 4,

or an oxime ether of the formula

where A and n are as defined above and R¹ and R² independently of oneanother are C₁–C₁₀ alkyl, C₁–C₁₀ alkoxy, C₅–C₁₀ cycloalkyl or C₅–C₁₀aryl, which may also contain from 1 to 3 nonadjacent nitrogen, oxygen orsulfur atoms in the carbon chain or in the carbon ring and may besubstituted by from 1 to 3 C₁–C₄ alkyl or alkoxy groups; R¹ or R² may bea hydrogen atom,

-   -   or R¹ and R² together form a bridge of from 2 to 14 carbon        atoms, it also being possible for some of the carbon atoms to be        part of an aromatic ring system.

The variables A in formulae I and II preferably comprise a hydrocarbonchain of from 2 to 8 carbon atoms and n is preferably 2.

The radicals R¹ and R² are each preferably a hydrogen atom, a C₁–C₆alkyl group or a C₁–C₆ alkoxy group. In the case of the hydrogen atoms,only one of the radicals, R¹ or R², may be a hydrogen atom.

Examples of suitable compounds containing amino groups includeethylenediamine, propylenediamine, tetramethylenediamine,pentamethylenediamine, hexamethylenediamine, diethylenetriamine,triethylenetetramine, polyethyleneimines, partially hydrolyzedpolyvinylformamides, ethylene oxide and propylene oxide adducts such asthe Texaco Jeffamines, cyclohexanediamine, and xylylenediamine.

The compound containing these functional groups may be added to thecomposition, or to the dispersion of the polymer, at any point in time.In the aqueous dispersion, there is still no crosslinking with the ketoor aldehyde groups. Only on drying does crosslinking take place on thecoated substrate.

The amount of the compound containing the functional groups ispreferably such that the molar ratio of the functional groups to theketo and/or aldehyde groups of the polymer is from 1:10 to 10:1, inparticular from 1:5 to 5:1, with particular preference from 1:2 to 2:1,and with very particular preference from 1:1.3 to 1.3:1.

In particular, equimolar amounts of the functional groups and the ketoand/or aldehyde groups are preferred.

The composition is used preferably as an adhesive, especially as anadhesive for bonding substrates of large surface area, i.e., forproducing laminates (laminating adhesive).

For this purpose, the composition may consist exclusively of the aqueousdispersion of the polymer, preferably with the addition of thefunctional-group compound dispersed or dissolved in the dispersion, and,where appropriate, photoinitiator (where it is not bonded to thepolymer). It may may comprise other additives, e.g., wetting agents,thickeners, protective colloids, light stabilizers, biocides, tackifiersor plasticizers.

Examples of suitable substrates for adhesive bonding are polymer films,in particular made from polyethylene or oriented polypropylene,polyamide, polyethylene terephthalate, cellulose acetate, cellophane,metalized (e.g., aluminum-coated (vapor-coated)) polymer film(abbreviated to metalized films) or else paper, card or metal foils, inparticular made from aluminum. The films and foils mentioned may alsohave been printed, e.g., with printing inks.

The laminating adhesive is applied to at least one large-surface-areasubstrate, preferably at a layer thickness of from 0.1 to 20 g/m²,particularly preferably from 2 to 15 g/m², e.g., by knife coating,brushing, etc.

At least one of the two substrates to be adhesive-bonded should betransparent to high-energy light, in particular UV light.

Preferably after drying or air-drying to remove the water in thedispersion (e.g., after from 1 to 60 seconds), the coated substrate maythen be laminated to a second substrate at a temperature of for examplefrom 20 to 200° C., preferably from 20 to 70° C., and at a pressure of,for example, from 1 to 30 N/m², preferably from 3 to 20 N/m².

The substrate coated with the adhesive preferably comprises atransparent polymer film.

The polymer or, respectively, the dispersion is preferably used as anadhesive for high gloss film lamination.

In high gloss film lamination, paper or card is adhesively bonded totransparent polymer films. The papers or cards may have been printed.

Directly after the adhesive bonding the laminating-adhesive layer may beirradiated, through the transparent film, with high-energy light, whichinitiates the crosslinking reactions of the photoinitiator group.

The light preferably used is UV light. The UV irradiation may be carriedout using commercially available medium-pressure mercury lamps or laserswhich emit in the UV region.

The energy radiated may, for example, be from 200 mJ/cm² to 2000 mJ/cm²,preferably from 500 mJ/cm² to 1000 mJ/cm² of irradiated area.

Immediately after the irradiation, further processing may take place,e.g., grooving or embossing of the laminated substrates, e.g., of thecards laminated with film. A waiting period is no longer required.

The novel laminating adhesive gives bonded substrates with high bondstrength, even in the region of grooves or embossments, and with hightransparency and high gloss. Their quality is affected little if at allby the storage time of the coated films.

EXAMPLES

A) Preparation

The preparation follows the general specification below:

The initial charge (180 g of water and 3.5 g of a styrene seed, 33%strength) was heated to an internal temperature of 90° C., and 10% offeed 2 was introduced initially. After 10 min, feed 1, which comprisesthe monomers, and feed 2 were started.

Feed 2 was composed of 67 g of sodium peroxodisulfate (2.5% 40strength). The composition of feed 1 in all cases is 78% butyl acrylate,20% methyl methacrylate and 2% acrylic acid. In the case of chemicalcrosslinking diacetone acylamide (DAAM) adipic dihydrazide (ADDH) DAAMis likewise present in the feed (see table). In the case ofphotocrosslinking a polymerizable photoinitiator can be presentoptionally in the feed.

Feeds 1 and 2 were metered in over 2 h and polymerization continued for0.5 h.

The amount of initiator (sodium peroxodisulfate) was in each case 0.3part by weight, and the emulsifier used comprised 0.5 part by weight ofDowfax® 2 A1 (alkyldiphenyloxide disulfonate) and 0.5 part by weight ofDisponil FES77 (sodium lauryl ether sulfate), based on the parts byweight of monomers stated in the table. The solids content was 55%.

In the case of benzophenone, the photoinitiator was stirred into the hotdispersion at 60° C. For chemical crosslinking, that is to sayDAAM-containing dispersions, after cooling, an aqueous solution of ADDHwas added. The mass ratio of ADDH to DAAM is, in all cases, 2:1.

B) High gloss film lamination

High gloss film lamination with card (Cromolux 70°) and polypropylene(corona-pretreated).

The pretreated side of the polypropylene film (PP) was coated withadhesive. After drying with cold air, the card was applied and rolled onusing a laboratory laminating roller. The laminated pieces cut to sizewere pressed in a roller press.

This was followed by direct irradiation with UV light (1000 MJ/cm²). Thelaminated specimens, after the time indicated in the table (immediate,30 minutes, 1 hour or 24 hours, see table), were grooved and/or embossed(grooving, fold in spine of book; embossing) and assessed after 6 weeks:

Grading: 1 Groove, embossing is very satisfactory

-   -   2 Groove, embossing has opened slightly at individual points,        detached    -   3 Groove, embossing has opened significantly at individual        points    -   4 Groove, embossing is completely open

TABLE Chemical crosslinking Photocrosslinking Dual crosslinking No. 1 23 4 5 6 7 8 9 10 11 12 13 14 15 DAAM 0.1 0.25 0.5 2.0 0 0 0 0 0.1 0.10.25 0.25 0.5 0.5 0.5 [pphm] Benzophenone 0 0 0 0 0.1 0.3 0.6 1.0 0.10.3 0.1 0.3 0.3 0.6 1.0 [pphm] Immediate 4/4 4/4 3/4 3/4 3/3 3/3 3/3 3/34/4 3/3 3/3 2/3 2/3 1-2/1- 1-/3 30 min 4/3 4/4 3/3 2/3 3/4 2/3 2/3 3-4/34/4 3-4/3 3/3 2/3 2-3/2 1-2/1- 1/2  1 h 4/4 3/4 3/3 1-2/3 3/4 3/3 3/33/3 4/3 2/3 2/3 1/3 1-2/2-3 1-/1- 1-/2 24 h 4/4 3/4 2-3/3 1/1 3/4 3/23/3 2-3/3 3/3 2/3 2/3 1/2 1-2/2-3 1/2 1-/1-2 The value before theoblique indicates the result of utilization, the value after the obliquethe result of embossing. It is clearly evident that the combination ofthe crosslinker systems is advantageous as compared with the use of anindividual crosslinker system, e.g. Variant 11 (with a total of just0.35 ppm crosslinker) attains the properties of version 3 (0.5 pphmcrosslinker). Variant 12 (with a total of 0.55 pphm crosslinker) exceedsthe properties of 3 (0.5 pphm crosslinker) and of 7 (0.6 pphmcrosslinker). Variant 14 (with a total of 1.1 pphm crosslinker) exceedsthe properties of 4 (pphm crosslinker).

1. A method of large-surface-area adhesive bonding of a UV-transparentfilm substrate to second substrate, which comprises: applying alaminating adhesive comprising: an aqueous polymer dispersion, whereina) the laminating adhesive comprises from 0.0001 to 0.5 mol of aphotoinitiator which on exposure to high-energy light causes acrosslinking reaction; and b) the polymer dispersed in the dispersionhas from 0.0001 to 1 mol of keto or aldehyde groups, the molar databeing based in each case on 100 g of the dispersed polymer to at leastone of the substrates to form an adhesive film; drying the adhesivefilm; adhesively bonding the substrates; and then exposing theUV-transparent film to high-energy light, wherein the second substratecomprises paper or card.
 2. The method as claimed in claim 1, whereinthe laminating adhesive is applied to at least one of the substrates ata thickness of from 0.1 to 20 g/m².
 3. The method as claimed in claim 1,wherein the high energy light is UV light.
 4. The method as claimed inclaim 1, wherein energy radiated by the high-energy light ranges from200 mJ/cm² to 2000 mJ/cm² of irradiated area.
 5. The method as claimedin claim 1, wherein after drying the substrate having the laminatingadhesive thereon, the substrate is bonded to the second substrate at atemperature ranging from 20 to 200° C.
 6. The method as claimed in claim1, wherein after drying the substrate having the laminating adhesivethereon, the substrate is bonded to the second substrate at a pressureranging from 1 to 30 N/m².
 7. The method as claimed in claim 1, whereinthe photoinitiator is bonded to the polymer.
 8. The method as claimed inclaim 1, wherein the photoinitiator comprises a benzophenone,acetophenone, a derivative of benzophenone or a derivative ofacetophenone.
 9. The method as claimed in claim 1, wherein thelaminating adhesive further comprises a compound containing at least twofunctional groups which undergo crosslinking with keto or aldehydegroups.
 10. The method as claimed in claim 9, wherein the amount of thecompound is from 0.0001 to 1 mol based on 100 g of the dispersedpolymer.
 11. The method as claimed in claim 9, wherein the functionalgroups of the compound comprise hydrazide, hydroxylamine, oxime ether oramino groups.
 12. The method as claimed in claim 1, wherein the polymeris composed of at least 40% by weight of principal monomers selectedfrom C1–C20 alkyl (meth)acrylates, vinyl esters of carboxylic acidscontaining up to 20 carbon atoms, vinylaromatics having up to 20 carbonatoms, ethylenically unsaturated nitriles, vinyl halides, vinyl ethersof alcohols containing from 1 to 10 carbon atoms, aliphatic hydrocarbonshaving from 2 to 8 carbon atoms and one or two double bonds, andmixtures of these monomers.
 13. The method as claimed in claim 1,wherein the polymer has a glass transition temperature of from −50° C.to 40° C.